I like it! I vaguely remember seeing something like that poster in a book once.

As for spamming, c'mon! Lots of business have nifty 404 error pages. Usually 'cause the web designer left 'em a gift. Sometimes it takes the company forever to even realize it's there. Not so much the large mainstream companies, usually the smaller ones just out having fun.

Unfortunately, the ones at larger companies get discovered by the execs, then they quietly disappear..... (shhhhh.)